Sigma-1 set
= Sigma-1 set
{c}
A set $A$ is in $\Sigma_1$ exactly when it is the domain of a partial computable function. Equivalently, there is a computable predicate $R$ such that
$$
x\in A\quad\Longleftrightarrow\quad\exists t\,R(x,t).
$$
= Sigma-1 set
{c}
A set $A$ is in $\Sigma_1$ exactly when it is the domain of a partial computable function. Equivalently, there is a computable predicate $R$ such that
$$
x\in A\quad\Longleftrightarrow\quad\exists t\,R(x,t).
$$